New tenant

[mfreeman451]

https://cloud.google.com/identity-platform/docs/multi-tenancy-managing-tenants

Our WebUI login flow needs to set/look for a cookie containing the tenantID so we dont burded the user too much on login with a 3rd field.

• [ ] API to create new tenant
• [ ] Use Firestore to manage tenants and members
• [ ] WebUI updates

Example firestore structure:

/tenants/{tenantId}
    /metadata { name, createdBy, ... }
    /members
        /{userId} { role, joinedDate, ... }